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Manual transmission fluid

I have a 1990 F350 7.3 diesel. I know for the 5 speed manual I need ATF fluid in it. I was wondering what you all have had luck with. Its kinda hard to shift so I'm wanting to smooth it out as best I can. Any suggestions on what to use would be greatly appreciated.

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dustybumpers

don't play well w others
I use Merc 5 in them . It works best because it is non-foaming.
 

Sparky83

Virginia Chapter member
5,566
219
Norlina NC
sometimes hard shifting can be a symptom of a couple different things.. Low fluid in the tranny, wrong fluid type, bad/worn out syncros, and not sure on the 90's but the 1st gen super dutys used a hydraulic clutch.. if not bled completely could result in weak effort being put against the clutch fork to disengage the trannys.. in my old truck with the muncie tranny i just ran straight gear oil.. yeah it cost me a little mileage over running ATF.. but didnt have to worry about lube issues..some of these newer trannys cant handle that though..
 

dustybumpers

don't play well w others
Can't use gear oil in a ZF. It won't go in gear.
His truck has a hydro clutch

Regular Mercon 5
Walmart sells it in qt bottles.
I think you need 3...... Maybe 3 1/2. Been a while.
 

Sparky83

Virginia Chapter member
5,566
219
Norlina NC
with the hydro clutch could still be an issue of air in the system there... could be worth a look in addition to the fluid change..
 

dustybumpers

don't play well w others
True. Not really a bleeding method, as you just sit in the truck, and just keep pushing the clutch in and pulling it back up.
Could take up to 100 pumps

If the clutch concentric ( main unit) is bad, it will bleed back down, causing it to be unable to put the transmission in reverse gear to begin with, then first, then the rest of the gears.

Usually the master cylinder is good.

Proper clutch "height" will be when the clutch pedal is "stiff" to within 1/2" from the top, allowing a "bump" of free play

ZF transmissions can be shifted without using the clutch when proper engine rpm range is reached
 

Sparky83

Virginia Chapter member
5,566
219
Norlina NC
True. Not really a bleeding method, as you just sit in the truck, and just keep pushing the clutch in and pulling it back up.
Could take up to 100 pumps

If the clutch concentric ( main unit) is bad, it will bleed back down, causing it to be unable to put the transmission in reverse gear to begin with, then first, then the rest of the gears.

Usually the master cylinder is good.

Proper clutch "height" will be when the clutch pedal is "stiff" to within 1/2" from the top, allowing a "bump" of free play

ZF transmissions can be shifted without using the clutch when proper engine rpm range is reached

my last truck had a bleeder nipple like the brakes have but was on the slave cylinder.. i hated bleeding that thing.. why i always tried to avoid disconnecting the line when i could.
 

dustybumpers

don't play well w others
Concentric on this truck is on the mainshaft inside the bell housing. Throw out bearing rides inside of it
There is a "nipple" that comes out beside the supply line, it could be mistaken for a bleeded, but it is not.
Some people push the pedal to the floor, and open this nipple, Then close it before raising the pedal
But it will break the seal inside, within a year, you will be replacing the concentric, it will not hold pressure over night.

When doing that, you might as well replace the plate, throw out bearing, pressure plate, and thrust bearing

I hate it that I can't post pictures here
 
Thank you guys! I'm probably going to go with some synthetic. I'm changing all my stuff over to it and everything runs smoother. So why not?!


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Fellro

Moderator
Staff member
Diesel ZF transmissions have an external slave, then fork and throwout bearing like the older style. As such, it is possible to see wear there as well. Low travel distance also will cause troubles, but as noted, the pedal feel will be low as well. Not so much an issue by 1990, but the earlier hydraulic clutches such as my 86 6.9 had firewall cracking issues that also led to not having full travel and then shifting problems.
 

dustybumpers

don't play well w others
My 92 IDI has it inside like the gas trucks.
My 94 power stroke is the same as the 92
 

Fellro

Moderator
Staff member
Last edited:

dustybumpers

don't play well w others
How did this go from what kid of fluid do I need to you and Sparky beating me to the ground?

It's bad enough I have to fight this fuking cancer, now I have to deal with pecking order too????????????

I quit this site.
I didn't belong here when I first joined, and it's obvious I don't belong now
I have 2 diesel trucks that have the concentric in the transmission. WHATEVER. WHO THE FUK CARES WHO IS RIGHT OR WRONG

I helped the guy, he is happy. PERIOD

Have a nice day boyzzzz
 
Last edited:
How did this go from what kid of fluid do I need to you and Sparky beating me to the ground?



It's bad enough I have to fight this fuking cancer, now I have to deal with pecking order too????????????



I quit this site.

I didn't belong here when I first joined, and it's obvious I don't belong now

I have 2 diesel trucks that have the concentric in the transmission. WHATEVER. WHO THE FUK CARES WHO IS RIGHT OR WRONG



I helped the guy, he is happy. PERIOD



Have a nice day boyzzzz



Synthetic Merc V....shifts great! 2nd and reverse were my problem gears and they haven't grounded since. The fluid I drained out smelled like old gear oil.


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Fellro

Moderator
Staff member
Zf transmissions definitely do not like 80-90. ATF all the way with them. My 88 gas has a hitch from 1st to 2nd when cold. Even trying an additive like Lucas didn't help, so I am guessing the synchro rings are damaged a little or something.
 

Sparky83

Virginia Chapter member
5,566
219
Norlina NC
wtf?? i wasnt attacking anyone... i was just throwing ideas out as to other possible causes since the OP mentioned a sluggish shifting.. nice to be called an attacker when i never was...
 
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New problem....now it'll barely go into gear. It's almost like the clutch won't bottom out and is always somewhat engaged.


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Sparky83

Virginia Chapter member
5,566
219
Norlina NC
sounds more like the initial problem you mentioned just got worse... since you stated that was the reason why you wanted to change the fluid... id say somethings up in the clutch system.. whether it be worn out, forks out of adjustment, air in the hydraulic clutch (as the others stated you had).. id be looking there for why its so hard to shift..
 

Fellro

Moderator
Staff member
Definitely sounds like a hydraulic problem. Also possible to just be a failed throwout, but that would also come with noise. The master cylinder fill is to the engine side of the brake booster.
 

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